REACTIONS
المؤلف:
Professor John W. Norbury
المصدر:
ELEMENTARY MECHANICS & THERMODYNAMICS
الجزء والصفحة:
p 126
28-12-2016
2686
REACTIONS
Remember that the total momentum 
of a system of particles was given by 
or
Up to now we have been measuring velocities with respect to the ''Lab" reference frame, which is the name for the reference frame associated with a stationary target. The Lab does not move, or in other words 
Lab = 0. We can also measure velocities with respect to the center of mass frame where cm = 0. This is also often called the center of momentum frame because if cm = 0 then 
. If = velocity in Lab frame and 
= velocity in cm frame then
Example A red billiard ball of mass mR moving at a speed vR collides head on with a black billiard ball of mass mB at rest. (A) What is the speed of the center of mass ? (B) What is the speed of both balls in the cm frame ?
Solution
which is the speed of the center of mass. Now get the speed of the red ball via
and the speed of the black ball is
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